Microwave electron tube device



Sept. 1, 1970 v TAKANORI OKOSHI ET AL 3,526,305

MICROWAVE ELECTRON TUBE DEVICE Filed April 24, 1968 5 Sheets-Sheet l M/HZO I 205 I TAKM/oe: OKDSH/a Ewen/ (ill/0;

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MICROWAVE ELECTRON TUBE DEVICE Sept. 1, 1970 5 Sheets-Sheet 5 Filed April 24, 1968 FiG.5

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United States Patent 3,526,805 MICROWAVE ELECTRON TUBE DEVICE Takanori Okoshi and Enbeng Chiu, Tokyo, Japan, assignors to Tokyo Shibaura Electric Co., Ltd., Kawasaki-shi, Japan, a corporation of Japan Filed Apr. 24, 1968, Ser. No. 723,831 Claims priority, application Japan, Apr. 27, 1967, 42/27,138 Int. Cl. H01 23/02 US. Cl. 315-5.38 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates to microwave electronic tubes, and more particularly to so-called O-type or linear beam microwave electronic tubes such as travelling-wave tubes, backward-wave tubes and klystrons.

In prior art O-type or linear beam microwave electronic tubes, electron beams radiated from an electron gun are collected by a collector consisting of a single collector electrode, through a microwave circuit. The collector electrode has applied thereto an electric potential substantially equal to the applied potential of the microwave circuit. Electrons inciding from the microwave circuit to the collector collide at high speeds with the collector electrode thereby generating heat therein, thus resulting in a high power loss at said electrode. On the other hand, when the collector voltage is lowered in order to decrease the collector loss, secondary electrons caused by high speed collision of electrons with the collector electrode will flow into the microwave circuit to produce ill effects upon the performance characteristics of the electron tube.

If electrons inciding into a collector which consists of a plurality of electrodes at various speeds with certain ranges of variation are collected quietly and at low speeds by means of any one of the electrodes corresponding to the speeds of said electrons, then the power dissipation in the collector will be reduced and the secondary electron emission will be avoided.

A principal object of this invention is to provide a high efficiency electron tube wherein power loss caused by collision of electrons with the collector is reduced.

SUMMARY OF THE INVENTION In accordance with this invention, there is provided a microwave electron tube device comprising an evacuated envelope, an electron gun provided at one end of said envelope and emitting electron beams, a microwave circuit structure disposed substantially in the middle part of said envelope and effecting an interaction with the electron beams, and a collector disposed at the other end of said envelope for collecting the electron beams travelling thereto. The collector includes a plurality of apertured electrode plates positioned at an inclined angle with respect to the axis of the envelope. Further provided is means to establish a substantially constant magnetic field substantially parallel to the axis of the en- "ice velope and means to establish a substantially constant electric field between the electrode plates. The magnetic and electric fields cause electrons to travel along a substantially parabolic trajectory and the electrode plates have openings along the lowest speed curve which corresponds to the minimum speed of the electrons in the axial direction of the envelope.

This invention will be more fully understood from the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a diagrammatic view illustrating the principles of this invention when applied to a travelling-wave tube;

FIG. 2 is a diagram illustrating the components of electric and magnetic fields applied to the collector of an electronic tube embodying this invention;

FIG. 3 is a graph showing trajectories of electrons incident on the collector of an electronic tube according to this invention and a curve joining the vertices of the electron trajectories;

FIG. 4 is a perspective view showing the collector of an electronic tube embodying this invention;

FIG. 5 is a graph which illustrates that electrons inciding into the collector as shown in FIG. 4 are apportioned to respective electrodes dependent upon the speeds thereof; and

FIG. 6 is a section showing one form of a collector according to this invention.

As shown in FIG. 1, within an evacuated envelope 11 made of glass are provided an electron gun 12, a microwave circuit structure 15 and a collector 19. Electrons emitted from a grounded cathode 13 of the electron gun 12 are formed into a beam by the action of first and second accelerating electrodes 14, and the electron beam enters the microwave circuit structure 15. While the electron beam having entered the microwave circuit structure 15 is travelling along the axis of a slow-wave structure 16 in the shape of a helix, it is subjected, as is well known, to the interaction of energy transfer between said electron beam and a signal electric wave propagating from an input terminal 17 to an output terminal 18. Thereafter, the electron beam flows into the collector 19. Along the outer peripheral surface of the evacuated glass envelope 11 is disposed a solenoid 21 which serves to provide a focussing magnetic field for focussing the electron beam along the axial direction of the slow-wave circuit structure 16. The collector 19 consists of five electrodes 20 20 20 20 and 20 Across adjacent ones of these electrodes are connected sources of power supply 22 22 22 and 22 so as to provide decelerating electric fields which respectively intersect with the incident electron beam at an angle defined therebetween and which are different in intensity from one another. Consequently, the beam-forming electrons incident on the collector are collected by any one of the collector electrodes dependent upon the speed thereof.

Referring to FIGS. 2 and 3, there will be described in detail the motion of electrons at the collector of the electronic tube according to this invention.

In FIGS. 2 and 3, the z-axis represents the direction of an electron beam entering the collector, viz. the axial direction of the tube. The x-axis in FIG. 2 is normal to, and into, the drawing plane, while the y-axis in FIG. 3 is normal to, and out of, the said plane. More than one electrode is disposed at the collector of the electron tube, the electrodes being oblique to the central axis z and parallel to one another, whereby a substantially uniform electric field E intersecting at an angle 0 with the central axis z is provided. The z-component E of the electric field E is formed so that the velocity of the electron beam may be reduced in the axial direction of the tube. In the direction of the tube axis, it is only required that a magnetic field is produced which is either substantially uniform or axially symmetrical with respect to the central axis. A uniform magnetic field B is produced in the embodiment. Such magnetic field may also be achieved by lengthening the focussing magnetic field of the electron beam to the collector section.

The motion of an electron in the intersected electric and magnetic fields as shown in FIG. 2, is given by the following equations of motion, wherein e represents the electronic charge and m the mass of the electron:

Solving these differential equations by locating the coordinate system so that initial conditions are, at t=0, a3:y=0, z V (the initial speed of an electron when entering the collector) and x=y=z=0,

where w is an angular frequency commonly called the cyclotron frequency and e w m B Where the magnetic field B is comparatively high, the cyclotron motions in Equations 4 and 5 will be negligible. Therefore, the motion of an electron can be dealt with in approximation as a two-dimension motion on xz plane. In this case, eliminating time 1 from Equations 4 and 6,

o e E -ac Such motion of electrons is illustrated in FIG. 3. Electrons having entered the collector at various speeds with certain variations follow trajectories 31, 32 and 33 in parabolic form as represented by Equation 8. At the vertices 34, 35 and 36 of the parabolas, the speed of electrons in the direction of the central axis z is zero. A locus 37 joining the vertices of the parabolas of Equation 8 becomes a parabola represented by:

This parabola will be hereinbelow termed the lowest speed curve.

Where incident electrons are collected at positions on the locus 37 represented by Equation 10, the electrons will have, at these collecting positions, only moving velocities directed laterally to the tube axis and having a magnitude of v The speed in the direction of the central axis 1 is zero, and the resultant velocity is minimized. The resultant velocity may be made remarkably smaller when compared with the velocity of incidence.

Equations 1 to are explained in, for example, Fundamentals of Electronic Motion Willis W. Harman, 1953, McGraw-Hill Book Co., Ltd.

In FIG. 4 there is shown an embodiment of a collector in accordance with the principles described above.

In FIG. 4, six electrode plates 41, 42, 43, 44, and 46 are arranged in parallel to one another and obliquely to the central axis 2 of the tube. The electrode plates 41 to 46 are made of copper, and are held in a manner to be electrically insulated from one another 'by means of insulative supportingrods 47, 48, 49 and 50, made for example, of ceramic material. Both ends of the supporting rods 47 to 50 are securely fixed to supporting fittings 51 and 52. An electron beam incides from a microwave circuit side 53 and passes through an opening 54 of the supporting fitting 51..The electrode plates 41,42,43, 44

and 45 are respectively formed with rectangular openings.

61, 62, 63, 64 and 65. Two sides along the x-axis of each of the rectangles are formed along the aforesaid lowest speed curve, while the height in the y direction of each rectangular opening is made so large as not to obstruct the motion of the electron beam. An opening 66 in the electrode plate 46, located at a central portion of said plate is utilized in manufacture to align the magnetic field to be produced by the magnetic field generating means so that the electron beam precisely travels along the tube axis.

The equation of the lowest speed curve as represented by Equation 10 can be rewritten L L QELME m 2E m 2E $111 0 (11) Rewriting the Equation 11 =2. 2 2. 2 2E cos 0 z m cot 0 B a:

The energy at incidence of an electron losing, at a position z, its speed in the direction of the tube axis is E -z E cos 6-2. By making the substitution V=E cos 0-z in Equation 12,

mined to be a fraction of a diameter of the electronic tube. The inclination 0 of the electric field or the inclination of the electrode plates with respect to the central axis z is determined by the above Equation 13 when the intensity of the focussing magnetic field is B Although it is desirable in principle to make the distance between adjacent electrode plates small and to increase the number of the electrode plates, it is preferable in manufacture to reduce the number for the purpose of applying electric potentials to the electrode plates.

Numerical values of the electrode plates in the embodiment are given in the following Table 1. The voltage of the microwave circuit is 2,000 v., the focusing magnetic field is 560 gauss, and the angle defined by the elec trode plate and the central axis z is 7220".

.Since the electron beam is focussed an opening sufficient for the electron beam to pass through is formed.

2 Sincev the aperture is made for alignment of a magnetic field to be produced, the dimensions may be suitably set.

The widths of the electrodes measured in the median xy plane are so chosen that the opening edges are located on the lowest speed curve, which in the present case is parabolic. In such an arrangement, electrons having entered from the microwave circuit structure are collected by the respective electrode plates at very low speeds compared with those at incidence, so that power loss at the collector is very low. Since the speed of electrons colliding with the collector electrode plates is low, the presence of secondary electrons is decreased. Furthermore, since secondary electrons emitted are moved at a speed v expressed by Equation 9 in the x direction perpendicular to the tube axis, they do not flow into the microwave circuit to produce any ill effect upon the performance of the tube.

FIG. illustrates how electrons are collected by the respective electrode plates as shown in the case where the electrode plates have electric potentials applied thereto indicated in Table l and where the microwave circuit structure has various voltages applied thereto. In FIG. 5, the abscissa represents in volts the applied voltage of the microwave circuit, while the ordinate represents in percent the ratio between the numbers of collected electrons and of incident electrons. As seen in FIG. 5, a state in which electrons are collected dependent upon the applied voltages of the microwave circuit by means of the electrode plates 41, 42, 43, 44, 45 and 46, is indicated by curves 71, 72, 73, 74, 75 and 76 respectively, drawn corresponding to the electrode plates 41, 42, 43, 44, 45 and 46. For example, when the applied voltage of the microwave circuit structure is about 1,000 v., 100% of the electrons are collected by means of the electrode plate 43 as shown by the curve 73.

The employment of the collector as described above, has improved the gross efficiency of the electron tube up to about 60% from 22.5% which was exhibited in the prior art.

In the above embodiment all the distances between adjacent electrode plates are equal. It is more preferable for collection of the electrons to, with the same number of electrode plates, set these distances smaller for electrodes located in regions where the energy of the incident electron beam is concentrated while larger at the other electrodes. The distribution of the electrons is concentrated in the middle portions of the tube and the spacing between adjacent electrodes is reduced in the middle portion since it is preferable, from the viewpoint of efficiency, to have uniform generation of energy by the electrodes.

In FIG. 6, a glass envelope 81 and a collector 82 of copper are sealed to each other.

An electron beam incides from a microwave circuit structure 84 on the left side as shown, passes through an electrode 85 in the shape of an obliquely cut cylinder, and is collected by the collector 82. To the collector 82 is attached a cooling fin 86 made of, for instance, copper. In the collector section of FIG. 6 there is provided a magnetic field in the direction of incidence of an elec tron beam and a decelerating electric field intersected with the electron beam, between the electrode 85 and the collector 82, as in the previous embodiment. Also in this arrangement, it is found that energy loss due to collisions of electrons with the collector 82 is decreased, thereby improving the efficiency. Returning electrons due to the secondary electron emission are prevented from flowing into the microwave circuit. The simple construction of the collector assures easy application of electric potentials to the electrodes.

Although in the above description it has been considered that the applied magnetic field is uniform along the central axis z, a non-uniform magnetic field produced when the collector is located at the end portion of the electron beam focusing solenoid may also be effective in practice so far as such magnetic field is substantially in axial symmetry with respect to the central axis z. By solving the equation of motion of electrons for magnetic field distributions, the lowest speed curves corresponding to the respective distributions may be determined.

It will be understood from the above description that an electron tube excellent in both efiiciency and performance characteristics can be provided by producing at the collector a decelerating electric field intersected with the axis of incidence of an electron beam in a magnetic field having a component in the direction of said axis of incidence. This effects deceleration in said axial direction as well as reduces lateral motion of the incident electrons, whereby each electron is collected by the collector at a speed much lower than that of incidence.

In order to focus the electron beam, a magnetic field produced by permanent magnets may be employed instead of the focusing solenoid. It is effective in the backwardwave tube and the travelling-wave tube to utilize a periodically alternating magnetic field as produced by arranging around the circumference of the tube a plurality of permanent magnets with pole pieces interposed between them by setting them alternately in different poles.

Although the invention has been described and illustrated in terms of preferred embodiments, it will be clear that it is not limited thereto, and that various modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A microwave electronic tube device comprising:

an evacuated envelope;

an electron gun disposed at one end of said envelope for emitting electron beams;

a microwave circuit structure disposed substantially in the middle portion of said envelope for interacting with said electron beams;

a collector disposed at the other end of said envelope for collecting the electron beams travelling thereto, said collector including a plurality of spaced, apertured, electrode plates, each positioned at an inclined angle with respect to the axis of said envelope;

means for establishing a substantially constant magnetic field substantially parallel to the axis of said envelope; and

means for establishing a substantially constant electric field against the incident electron beams between said electrode plates;

said magnetic and electric fields causing the electrons of said electron beams to move along substantially parabolic trajectories; and

said apertured electrode plates having openings along the lowest speed curve which corresponds to the minimum speed of said electrons in the direction of the axis of said envelope.

2. A microwave electronic tube device according to claim 1, wherein said magnetic field is substantially uniform over the collector region, and the shape of the lowest speed curve along which the apertures of the electrode plates are provided is substantially parabolic.

3. A microwave electronic tube device according to claim 1 wherein said electrode plates are electrically insulated from one another.

4. A microwave electron tube device according to claim 2, wherein said plurality of electrode plates are disposed at substantially equal intervals and substantially in parallel with one another.

5. A microwave electron tube device according to claim 2, wherein said plurality of electrode plates are disposed substantially in parallel with one another, and wherein the intervals between adjacent ones of said electrode plates are smaller at the middle portions than at the end portions of said collector.

References Cited UNITED STATES PATENTS 3,175,120 3/1965 Wendt 3l55.38

RAYMOND F. HOSSFELD, Primary Examiner US. Cl. X.R. 315--3.5 

